Implement float -> small int cast

Also workaround small signed int eq/ne binop clif bug

example/mini_core.rs

@@ -52,6 +52,7 @@ unsafe impl Copy for i8 {}
 unsafe impl Copy for i16 {}
 unsafe impl Copy for i32 {}
 unsafe impl Copy for isize {}
+unsafe impl Copy for f32 {}
 unsafe impl Copy for char {}
 unsafe impl<'a, T: ?Sized> Copy for &'a T {}
 unsafe impl<T: ?Sized> Copy for *const T {}
@@ -277,6 +278,15 @@ impl PartialEq for usize {
     }
 }
 
+impl PartialEq for i8 {
+    fn eq(&self, other: &i8) -> bool {
+        (*self) == (*other)
+    }
+    fn ne(&self, other: &i8) -> bool {
+        (*self) != (*other)
+    }
+}
+
 impl PartialEq for i32 {
     fn eq(&self, other: &i32) -> bool {
         (*self) == (*other)
@@ -344,6 +354,14 @@ impl Neg for isize {
     }
 }
 
+impl Neg for f32 {
+    type Output = f32;
+
+    fn neg(self) -> f32 {
+        -self
+    }
+}
+
 pub enum Option<T> {
     Some(T),
     None,

example/mini_core_hello_world.rs

@@ -250,4 +250,10 @@ fn main() {
     unsafe { assert_eq!(ABC as usize, 0); }
 
     &mut (|| Some(0 as *const ())) as &mut dyn FnMut() -> Option<*const ()>;
+
+    let f = 1000.0;
+    assert_eq!(f as u8, 255);
+    let f2 = -1000.0;
+    assert_eq!(f2 as i8, -128);
+    assert_eq!(f2 as u8, 0);
 }

src/base.rs

@@ -334,11 +334,7 @@ fn trans_stmt<'a, 'tcx: 'a>(
                     let lhs = trans_operand(fx, lhs);
                     let rhs = trans_operand(fx, rhs);
 
-                    let signed = match ty.sty {
-                        ty::Uint(_) => false,
-                        ty::Int(_) => true,
-                        _ => unimplemented!("checked binop {:?} for {:?}", bin_op, ty),
-                    };
+                    let signed = type_sign(ty);
 
                     let res = if !fx.tcx.sess.overflow_checks() {
                         let val = trans_int_binop(fx, *bin_op, lhs, rhs, lhs.layout().ty, signed).load_scalar(fx);
@@ -444,14 +440,7 @@ fn trans_stmt<'a, 'tcx: 'a>(
                         let to_clif_ty = fx.clif_type(to_ty).unwrap();
                         let from = operand.load_scalar(fx);
 
-                        let signed = match from_ty.sty {
-                            ty::Ref(..) | ty::RawPtr(..) | ty::FnPtr(..) | ty::Char | ty::Uint(..) | ty::Bool => false,
-                            ty::Int(..) => true,
-                            ty::Float(..) => false, // `signed` is unused for floats
-                            _ => panic!("{}", from_ty),
-                        };
-
-                        let res = clif_int_or_float_cast(fx, from, to_clif_ty, signed);
+                        let res = clif_int_or_float_cast(fx, from, type_sign(from_ty), to_clif_ty, type_sign(to_ty));
                         lval.write_cvalue(fx, CValue::by_val(res, dest_layout));
                     }
                 }
@@ -809,6 +798,21 @@ pub fn trans_int_binop<'a, 'tcx: 'a>(
         return res;
     }
 
+    let (lhs, rhs) = if
+        (bin_op == BinOp::Eq || bin_op == BinOp::Ne)
+        && (lhs.layout().ty.sty == fx.tcx.types.i8.sty || lhs.layout().ty.sty == fx.tcx.types.i16.sty)
+    {
+        // FIXME(CraneStation/cranelift#896) icmp_imm.i8/i16 with eq/ne for signed ints is implemented wrong.
+        let lhs = lhs.load_scalar(fx);
+        let rhs = rhs.load_scalar(fx);
+        (
+            CValue::by_val(fx.bcx.ins().sextend(types::I32, lhs), fx.layout_of(fx.tcx.types.i32)),
+            CValue::by_val(fx.bcx.ins().sextend(types::I32, rhs), fx.layout_of(fx.tcx.types.i32)),
+        )
+    } else {
+        (lhs, rhs)
+    };
+
     binop_match! {
         fx, bin_op, signed, lhs, rhs, out_ty, "int/uint";
         Add (_) iadd;

src/cast.rs

@@ -49,8 +49,9 @@ pub fn clif_intcast<'a, 'tcx: 'a>(
 pub fn clif_int_or_float_cast(
     fx: &mut FunctionCx<'_, '_, impl Backend>,
     from: Value,
+    from_signed: bool,
     to_ty: Type,
-    signed: bool,
+    to_signed: bool,
 ) -> Value {
     let from_ty = fx.bcx.func.dfg.value_type(from);
 
@@ -60,21 +61,56 @@ pub fn clif_int_or_float_cast(
             fx,
             from,
             to_ty,
-            signed,
+            from_signed, // FIXME is this correct?
         )
     } else if from_ty.is_int() && to_ty.is_float() {
         // int-like -> float
-        if signed {
+        if from_signed {
             fx.bcx.ins().fcvt_from_sint(to_ty, from)
         } else {
             fx.bcx.ins().fcvt_from_uint(to_ty, from)
         }
     } else if from_ty.is_float() && to_ty.is_int() {
         // float -> int-like
-        if signed {
-            fx.bcx.ins().fcvt_to_sint_sat(to_ty, from)
+        if to_ty == types::I8 || to_ty == types::I16 {
+            // FIXME implement fcbt_to_*int_sat.i8/i16
+            let val = if to_signed {
+                fx.bcx.ins().fcvt_to_sint_sat(types::I32, from)
+            } else {
+                fx.bcx.ins().fcvt_to_uint_sat(types::I32, from)
+            };
+            let (min, max) = type_min_max_value(to_ty, to_signed);
+            let min_val = fx.bcx.ins().iconst(types::I32, min);
+            let max_val = fx.bcx.ins().iconst(types::I32, max);
+
+            let val = if to_signed {
+                let has_underflow = fx.bcx.ins().icmp_imm(
+                    IntCC::SignedLessThan,
+                    val,
+                    min,
+                );
+                let has_overflow = fx.bcx.ins().icmp_imm(
+                    IntCC::SignedGreaterThan,
+                    val,
+                    max,
+                );
+                let bottom_capped = fx.bcx.ins().select(has_underflow, min_val, val);
+                fx.bcx.ins().select(has_overflow, max_val, bottom_capped)
+            } else {
+                let has_overflow = fx.bcx.ins().icmp_imm(
+                    IntCC::UnsignedGreaterThan,
+                    val,
+                    max,
+                );
+                fx.bcx.ins().select(has_overflow, max_val, val)
+            };
+            fx.bcx.ins().ireduce(to_ty, val)
         } else {
-            fx.bcx.ins().fcvt_to_uint_sat(to_ty, from)
+            if to_signed {
+                fx.bcx.ins().fcvt_to_sint_sat(to_ty, from)
+            } else {
+                fx.bcx.ins().fcvt_to_uint_sat(to_ty, from)
+            }
         }
     } else if from_ty.is_float() && to_ty.is_float() {
         // float -> float

src/common.rs

@@ -116,74 +116,46 @@ pub fn resolve_value_imm(func: &Function, val: Value) -> Option<u128> {
     }
 }
 
-pub fn type_min_max_value<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> (i64, i64) {
-    use syntax::ast::UintTy::*;
-    use syntax::ast::IntTy::*;
-
-    let uint_usize_cvt = |uint| {
-        match uint {
-            UintTy::Usize => match pointer_ty(tcx) {
-                types::I16 => UintTy::U16,
-                types::I32 => UintTy::U32,
-                types::I64 => UintTy::U64,
-                ty => unreachable!("{:?}", ty),
-            }
-            _ => uint,
-        }
-    };
-
-    let int_isize_cvt = |int| {
-        match int {
-            IntTy::Isize => match pointer_ty(tcx) {
-                types::I16 => IntTy::I16,
-                types::I32 => IntTy::I32,
-                types::I64 => IntTy::I64,
-                ty => unreachable!("{:?}", ty),
-            }
-            _ => int,
-        }
-    };
-
-    let min = match ty.sty {
-        ty::Uint(uint) => match uint_usize_cvt(uint) {
-            U8 | U16 | U32 | U64 => 0i64,
-            U128 => unimplemented!(),
-            Usize => unreachable!(),
-        }
-        ty::Int(int) => match int_isize_cvt(int) {
-            I8 => i8::min_value() as i64,
-            I16 => i16::min_value() as i64,
-            I32 => i32::min_value() as i64,
-            I64 => i64::min_value(),
-            I128 => unimplemented!(),
-            Isize => unreachable!(),
-        }
+pub fn type_min_max_value(ty: Type, signed: bool) -> (i64, i64) {
+    assert!(ty.is_int());
+    let min = match (ty, signed) {
+        (types::I8 , false)
+        | (types::I16, false)
+        | (types::I32, false)
+        | (types::I64, false) => 0i64,
+        (types::I8, true) => i8::min_value() as i64,
+        (types::I16, true) => i16::min_value() as i64,
+        (types::I32, true) => i32::min_value() as i64,
+        (types::I64, true) => i64::min_value(),
+        (types::I128, _) => unimplemented!(),
         _ => unreachable!(),
     };
 
-    let max = match ty.sty {
-        ty::Uint(uint) => match uint_usize_cvt(uint) {
-            U8 => u8::max_value() as i64,
-            U16 => u16::max_value() as i64,
-            U32 => u32::max_value() as i64,
-            U64 => u64::max_value() as i64,
-            U128 => unimplemented!(),
-            Usize => unreachable!(),
-        }
-        ty::Int(int) => match int_isize_cvt(int) {
-            I8 => i8::max_value() as i64,
-            I16 => i16::max_value() as i64,
-            I32 => i32::max_value() as i64,
-            I64 => i64::max_value(),
-            I128 => unimplemented!(),
-            Isize => unreachable!(),
-        }
+    let max = match (ty, signed) {
+        (types::I8, false) => u8::max_value() as i64,
+        (types::I16, false) => u16::max_value() as i64,
+        (types::I32, false) => u32::max_value() as i64,
+        (types::I64, false) => u64::max_value() as i64,
+        (types::I8, true) => i8::max_value() as i64,
+        (types::I16, true) => i16::max_value() as i64,
+        (types::I32, true) => i32::max_value() as i64,
+        (types::I64, true) => i64::max_value(),
+        (types::I128, _) => unimplemented!(),
         _ => unreachable!(),
     };
 
     (min, max)
 }
 
+pub fn type_sign(ty: Ty<'_>) -> bool {
+    match ty.sty {
+        ty::Ref(..) | ty::RawPtr(..) | ty::FnPtr(..) | ty::Char | ty::Uint(..) | ty::Bool => false,
+        ty::Int(..) => true,
+        ty::Float(..) => false, // `signed` is unused for floats
+        _ => panic!("{}", ty),
+    }
+}
+
 pub struct FunctionCx<'a, 'tcx: 'a, B: Backend> {
     // FIXME use a reference to `CodegenCx` instead of `tcx`, `module` and `constants` and `caches`
     pub tcx: TyCtxt<'tcx>,

src/intrinsics.rs

@@ -473,19 +473,13 @@ pub fn codegen_intrinsic_call<'a, 'tcx: 'a>(
                 _ => unimplemented!("intrinsic {}", intrinsic),
             };
 
-            let signed = match T.sty {
-                ty::Uint(_) => false,
-                ty::Int(_) => true,
-                _ => unimplemented!("{} for {:?}", intrinsic, T),
-            };
-
             let res = crate::base::trans_checked_int_binop(
                 fx,
                 bin_op,
                 x,
                 y,
                 ret.layout().ty,
-                signed,
+                type_sign(T),
             );
             ret.write_cvalue(fx, res);
         };
@@ -497,25 +491,14 @@ pub fn codegen_intrinsic_call<'a, 'tcx: 'a>(
                 "overflowing_mul" => BinOp::Mul,
                 _ => unimplemented!("intrinsic {}", intrinsic),
             };
-            let res = match T.sty {
-                ty::Uint(_) => crate::base::trans_int_binop(
-                    fx,
-                    bin_op,
-                    x,
-                    y,
-                    ret.layout().ty,
-                    false,
-                ),
-                ty::Int(_) => crate::base::trans_int_binop(
-                    fx,
-                    bin_op,
-                    x,
-                    y,
-                    ret.layout().ty,
-                    true,
-                ),
-                _ => panic!(),
-            };
+            let res = crate::base::trans_int_binop(
+                fx,
+                bin_op,
+                x,
+                y,
+                ret.layout().ty,
+                type_sign(T),
+            );
             ret.write_cvalue(fx, res);
         };
         _ if intrinsic.starts_with("saturating_"), <T> (c x, c y) {
@@ -527,11 +510,7 @@ pub fn codegen_intrinsic_call<'a, 'tcx: 'a>(
                 _ => unimplemented!("intrinsic {}", intrinsic),
             };
 
-            let signed = match T.sty {
-                ty::Uint(_) => false,
-                ty::Int(_) => true,
-                _ => unimplemented!("{} for {:?}", intrinsic, T),
-            };
+            let signed = type_sign(T);
 
             let checked_res = crate::base::trans_checked_int_binop(
                 fx,
@@ -548,7 +527,7 @@ pub fn codegen_intrinsic_call<'a, 'tcx: 'a>(
             // `select.i8` is not implemented by Cranelift.
             let has_overflow = fx.bcx.ins().uextend(types::I32, has_overflow);
 
-            let (min, max) = type_min_max_value(fx.tcx, T);
+            let (min, max) = type_min_max_value(clif_ty, signed);
             let min = fx.bcx.ins().iconst(clif_ty, min);
             let max = fx.bcx.ins().iconst(clif_ty, max);
 
@@ -879,18 +858,14 @@ pub fn codegen_intrinsic_call<'a, 'tcx: 'a>(
 
             let ret_lane_ty = fx.clif_type(ret_lane_layout.ty).unwrap();
 
-            let signed = match lane_layout.ty.sty {
-                ty::Uint(..) => false,
-                ty::Int(..) => true,
-                ty::Float(..) => false, // `signed` is unused for floats
-                _ => panic!("{}", lane_layout.ty),
-            };
+            let from_signed = type_sign(lane_layout.ty);
+            let to_signed = type_sign(ret_lane_layout.ty);
 
             for lane in 0..lane_count {
                 let lane = mir::Field::new(lane.try_into().unwrap());
 
                 let a_lane = a.value_field(fx, lane).load_scalar(fx);
-                let res = clif_int_or_float_cast(fx, a_lane, ret_lane_ty, signed);
+                let res = clif_int_or_float_cast(fx, a_lane, from_signed, ret_lane_ty, to_signed);
                 ret.place_field(fx, lane).write_cvalue(fx, CValue::by_val(res, ret_lane_layout));
             }
         };